Octahedral MnO 2 molecular sieve (OMS) was prepared using hydrothermal synthesis route in the absence and in the presence of urea. OMS was also prepared by solvent free method.Catalysts were characterized by the complementary combination of X-ray diffraction, N 2adsorption, scanning electron microscope, UV-visible spectroscopy, thermo gravimetric analysis, and NH 3 & CO 2 temperature programmed desorption techniques. Catalysts were investigated in the oxidation of benzyl alcohols, hydration of aromatic/heterocyclic nitrile and condensation reactions (Knoevenagel and Aldol). Furthermore, applicability of the catalyst was extended in one-pot tandem conversion of benzyl alcohol to 2-benzylidenemalononitrile, (E)-chalcone, and 2,3-dihydro-1,5-benzothiazepine. 2-Benzylidenemalononitrile and (E)-chalcone were prepared by two steps tandem reactions from benzyl alcohol, whereas 2,3-dihydro-1,5-benzothiazepine was prepared by three steps tandem reaction from benzyl alcohol. Recycling study show that no significant decrease in the catalytic activity was observed even after five recycles. To the best of our knowledge, this is the first report, which shows that OMS materials obtained using different synthesis methods exhibited significant difference in the catalytic activity in the above mentioned reactions. flask fitted with a condenser. Product was filtered, washed with deionised water, and dried at 120 C for 8-10 h. Material is designated as OMS-2 (Yield = 80%).
Synthesis of OMS-2 by solvent free methodOMS-2 was prepared under solvent free condition by following the reported procedure. 33 In a typical synthesis, 2.37 g KMnO 4 (0.06 mol) and 5.51 g (0.09 mol) of Mn(Ac) 2 .4H 2 O were mixed and grounded in a mortar. The mixed powder was kept in a Teflon lined autoclave at 120C for 12 h. The resulting black product was thoroughly washed with deionised water to remove any ions which may remain in the product, and dried at 120C for 8-10 h. Material is designated as OMS-2-SF (Yield = 56 %).
Hydrothermal synthesis of OMS-2 using urea 8 mmol of KMnO 4 (1.26 g) was dissolved in 20 mL of deionised water. 28 mmol urea (1.68 g) was added (in 15 minutes) to the solution and the reaction mixture was stirred for 30 minutes at ambient condition. After 30 min, resulting solution was added drop wise to a vigorously stirred mixture of MnSO 4 .H 2 O (10.5 mmol, 1.77 g in 6 mL water) and conc. HNO 3 (0.6 mL). The reaction mixture was refluxed for 24 h in a round bottom glass flask fitted with a condenser. Product was filtered, washed with deionised water, and dried at 120C for 8-10 h. OMS-2 material prepared with urea is designated as OMS-2-U (Yield = 99 %). Catalyst characterizations X-ray diffraction (XRD) patterns were recorded in the 2θ range of 5-80° with a scan speed of 2°/min on a PANalytical X'PERT PRO diffractometer using Cu Kα radiation (λ=0.1542 nm, 40 kV, 40 mA) and a proportional counter detector. Nitrogen adsorption measurements were performed at -200C by Quantachrome Instruments, Autosorb-IQ volumetric adsorption analyzer....
